Data communication devices (DCDs) are used for data communications between terminals or computers over data lines such as dial-up and dedicated telephone lines. These DCDs include modems, terminal adapters, and digital service equipment. DCDs should be isolated from high voltages that may occur on the data lines. Considering the damage that high voltage can cause the low voltage electronics residing in the DCDs, it is necessary to isolate the low voltage electronics from high voltages. This requirement is set forth in equipment specifications such as Underwriters Laboratory 1459 and Bellcore Technical Reference TR-NWT-001089.
The methods currently used for isolation include transformers and high-voltage capacitors. Both these methods are unsatisfactory. Line isolation based on the use of transformers depends on the enamel coating on the magnet wire windings to provide protection. This enamel coating adversely affects the telecommunications signals due to the leakage inductance associated with wire to wire spacing. The transformers used are relatively large and expensive components of the data communications equipment. Because high-voltage capacitors must provide a low impedance to the data signal, they tend to be physically large.
An improved method of isolating DCDs from the data lines that will also reduce size and cost is desirable.